Higher category theory

higher category theory

Basic concepts

Basic theorems





Universal constructions

Extra properties and structure

1-categorical presentations



An nn-poset is any of several concepts that generalize posets in higher category theory. In fact, nn-posets are the same as (n1,n)(n-1,n)-categories.


Fix a meaning of \infty-category, however weak or strict you wish. Then an nn-poset is an \infty-category such that all parallel pairs of jj-morphisms are equivalent for jnj \geq n. Thus, up to equivalence, there is no point in mentioning anything beyond nn-morphisms, not even whether two given parallel nn-morphisms are equivalent. This definition makes sense as low as n=1n = -1; the statement that parallel (1)(-1)-morphisms are equivalent simply means that there exists an object (a 00-morphism).

Special cases

In the light of the general definition, one must interpret ‘is’ up to equivalence of categories. The last statement also depends on how strict your definition of \infty-category or nn-category is; it is actually simpler to define nn-posets from scratch as given above than to define them in terms of nn-categories.

Basic theorems

The \infty-category of (small) nn-posets, as a full sub-∞-category of the \infty-category of \infty-categories, is an (n+1)(n+1)-poset. That is, nn-posets form an (n+1)(n+1)-poset. This is well known for small values of nn.

Last revised on October 13, 2011 at 00:40:31. See the history of this page for a list of all contributions to it.